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Crossposting from Metabunk with permission from the thread opener marko.posavec.

photo by Metabunk user marko.posavec

Their photo shows British Airways Boeing 777-300ER G-STBF in flight with something producing a contrail or the like from the outboard side of #1 engine.

What is/could be causing this?

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  • $\begingroup$ It might simply be that the de-icing is on and that is melting ice from the cowl's lips $\endgroup$
    – sophit
    Commented Jul 30, 2023 at 16:01
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    $\begingroup$ Ice and de-ice at 36000 ft? $\endgroup$ Commented Jul 30, 2023 at 16:03
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    $\begingroup$ Proof positive that the chemtrail phenomenon is real :; $\endgroup$ Commented Jul 30, 2023 at 16:03
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    $\begingroup$ Wild hypothesis: some sort of un-evenness in cowl / nacelle that is causing turbulence and triggering condensation? $\endgroup$ Commented Jul 30, 2023 at 16:05
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    $\begingroup$ Cowls are are evaporatively anti-iced. They are kept above the boiling point so supercooled waterdroplets turn to steam right away on contact. If ice formation is allowed, it can damage blades. $\endgroup$
    – John K
    Commented Jul 30, 2023 at 17:45

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Well, it's not condensate water from the tail pipe, and it looks to be originating from the main cowl, so it can only be one of the Big Three fluids; fuel, engine oil, or hydraulic oil (for the reversers, assuming they're hydraulically driven). Such leaks are not unheard of.

If I was flying 2000 ft below them on the same track so that I was able to observe that for a while, I'd probably contact ATC to relay to them my observations.

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  • $\begingroup$ This was taken when the aircraft crossed Romania inbound LHR from BOM, so it probably had been ongoing for a while, or would it start mid-flight? In any case, the flight didn't divert and the aircraft remained in service for another flight about 3 hrs after landing. So at least it wasn't as dire as the Air Transat one. $\endgroup$ Commented Jul 30, 2023 at 15:53
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    $\begingroup$ re "so it can only be one of the Big Three fluids" -- consider aviation.stackexchange.com/questions/100213/… $\endgroup$ Commented Jul 30, 2023 at 16:08
  • $\begingroup$ Yes of course. Does anyone have the QRH for these three leaks at their fingertips? I'm cut off from mine for another couple of days... probably not far off from "land nearest suitable" for some of these, right? $\endgroup$ Commented Jul 30, 2023 at 16:15
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    $\begingroup$ Possibly a leak could make a noticeable contrail and be too small to even notice fuel quantity wise and go undetected for a while. Or possibly it's just a fluid like engine oil venting off for some reason. $\endgroup$
    – John K
    Commented Jul 30, 2023 at 17:50

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